Back in 2003, I wrote a column about saltwater aquariums, specifically about keeping clown fish. The movie “Finding Nemo” had just been released and children wanted their own little Nemo. At the time, that worried me because I was afraid people wouldn’t be able to properly care for the fish.

I talked to the people at Clearwater Aquarium and found out that a saltwater aquarium isn’t as difficult to set up and maintain as I had feared. You need a heater and a filter, just like a fresh water aquarium, and beyond that, you need to test the water periodically to make sure the proper level of salinity is maintained. That’s it. That information made me feel a bit better, because if a family is willing to have an aquarium, it isn’t that much harder to have a good home for “Nemo.”

The woman I talked to explained that when someone wants to start a saltwater aquarium, they buy the tank, heater, filter and testing kit, get everything running, and then gradually add the marine salt. When the tank is ready for fish, in about a week, they are sold damselfish because damselfish are very hardy and can withstand more changes in their environment than many other fish. After six to eight weeks, the system should be stable enough to add other varieties of fish.

Because of the length of time needed to set up the tank, many stores in 2003 sold “Finding Nemo” kits, which were already marine fish friendly. They consisted of a 12-gallon tank, complete with salt water, one clown fish, two blue damsels and a hermit crab.

Unfortunately, if you’ve just taken children to see “Finding Dory,” and they are now asking for “Dory,” you’ll find that the blue tang is, well, a different kettle of fish. Also known as the blue barber, the blue doctor, and the blue tang surgeonfish, this fish has scalpel-sharp fins and tail that they use for protection when threatened.

They are not recommended for beginners and take considerably more care than the clown fish. They are a much larger fish, growing to about a foot in length. (Clown fish are about three inches long). While a 12-gallon tank may be fine for the clown fish, the blue tang needs a 100- to 180-gallon tank. That’s at least a six-foot tank. Dory needs way more real estate than Nemo. If you want multiple fish, you’ll need a proportionately larger tank.

Also, blue tangs have never been successfully bred in captivity, so if you buy a blue tang, you’re buying a fish taken from the wild. Since a primary food for blue tangs is algae that grow on coral reefs, which prevents the algae from overgrowing and suffocating the coral, taking too many from one area can threaten the life of the reef. Another threat to the coral reef is the cyanide that is frequently used to stun the fish so they can be captured.

Because the blue tang doesn’t eat typical fish food, you need to make sure it gets a special diet. No fast sprinkle of dry fish food to maintain the blue tang. They need an algae-heavy diet.

If you do decide to buy a blue tang, prepare to pay between $50 and $100 dollars a fish. Since they are not recommended for beginners, one Internet site suggests two similar-looking fish, the saltwater yellowtail damselfish, or the freshwater, boesemani rainbow.

When setting up an aquarium, choose the location carefully. Direct sunlight can change the water temperature and endanger the fish. The same is true if the aquarium is too near a heat source in winter. Make sure the location doesn’t get too cold during winter months, as too cold is as bad as too hot.

Some fish get along quite well with other fish, but some fish can be aquatic bullies, biting at other fish and tearing their fins. Some fish only beat up others of the same species. Whether you choose to have a saltwater, or a freshwater aquarium, read about the best combinations of fish before you invest in a tank and all the accessories.

Also, make sure you have the time needed to properly care for the fish. Children mean well, but they may not be as conscientious about cleaning the tank or feeding the fish, as they should be. Forgetting to test for the proper level of salt could mean dead pets. There should be an adult who is ultimately responsible for the welfare of the fish.